Maximum Suck

[Fat Guy]

by David Scantland

 

Your home is full of holes.

 

Buildings must breathe; occupants need fresh air; combustion in furnaces and appliances requires oxygen. It's a passive principle of building design that doesn't require much attention. Since most of us don't live in pressurized capsules, we take it for granted that the air pressure outside the home will equal the pressure inside. And this is the job of holes. When air is expelled via one hole, new air rushes in through another to replace it. So your home is full of them. And it's a good thing, in exactly the same way that not having a tornado outside your front door is a good thing.

 

Try this. Take a shoebox and seal its lid with heavy tape. Cut a hole in the side just large enough to accept the hose from your vacuum cleaner. Stick the hose in just a little way, seal the edges, and turn on the vacuum. Depending on the power of the appliance and the resilience of the box, your results may vary, but one thing will be clear: the box is subjected to considerable negative pressure and threatens to collapse. This is what happens when the occasional twister sidles up to the old family domicile. It's why meteorologists advise opening windows despite the heavy rain that accompanies violent storms: better a few damp carpets than a pile of wet kindling. But to a lesser degree, it's also what happens when you punch the "on" button on the exhaust hood over (or behind) your cooktop. The air it expels must be replaced.

Since the energy shocks of the '70s and '80s, buildings have been constructed with tighter joints, more insulation, more efficient insulation, and greater attention to weather-stripping and air-tight glazing. All of this means fewer holes.

 

An increasing affinity for high-output ranges, downdraft cooktops, and the idea that the way kitchens look is as important as how well they work, have led to an increase in home ventilating power.

In the US, at least, there is no standard for how much ventilation should be applied for a given size or output of range. In a way this is understandable. Ventilation fans should remove smoke and odor, but the size of your stove, the BTUs it generates, and the amount of smoke and odor you create when using it are not necessarily related. Even if you're a serious cook, the relationship is tenuous. You can simmer a stock all day and not have a problem. You might not want to ventilate some aromas: a loaf of baking bread, a gently bubbling soup, or a whiff of onions in butter or olive oil can make a house a home. But neglect three measly bacon strips -- whether the pan is on a five-inch electrical coil or a multi-ring 18K BTU burner -- for just a moment, and you can fill the house with the airborne effluent of carbonized fat and flesh that will linger for days.

 

Blowin' in the wind

 

You would be forgiven for wondering why this topic has consumed my attention. Here's why: at Chez Dave, an unassuming but apparently magical dry-erase board accretes a roster of chores throughout the week. As it is a project that had been discussed in a shallow but persistent manner, and as there was an inexplicable surplus in the Christmas budget (as yet undiminished by an offspring-tendered petition for a mondo subwoofer), I am not surprised when the following item appears:

 

Replace kitchen fan

 

There is good reason to consider the appeal since three members of the household suffer from either asthma or respiratory allergies. Inadequate kitchen ventilation not only aggravates the situation, it makes a burnt omelette too hard to conceal. So I agreed to research the problem. Research is the essential first step in all home remodeling projects. Not only does it help focus project parameters, delineate the budget, and avert mishaps, it is also a great way to postpone actual work.

 

My first question was: why didn't the present fan work very well? There were two possibilities: either the fan was underpowered or the fan was too small to pull smoke from the entire surface of the stove.

 

Like many suburban houses, ours came with a built-in exhaust fan over the stove. It is white; its 30-inch width is the same as the width of the range. The fan is 5 inches in diameter and is mounted behind a removable, metal mesh filter. The filter and fan are in a 10-inch square casing set in the center of the hood. A label inside the hood says that the fan moves 160 cubic feet per minute (CFM).

The range is 25 3/4 inches deep, but the front edge is about 27 inches out from the wall. The edge of the largest burner is 24 inches out, and the hood is 17 inches deep. Is it reasonable to assume that the fan can remove smoke from that far away? How strong a pull is 160 CFM?

 

According to the Broan-NuTone Group, the world's largest manufacturer of residential ventilation products:

For conventional electric and gas ranges or cook tops, we offer a complete line of hoods that can fit your cooking needs with features you desire. For high output gas ranges or cooktops, the minimum rate of 1 CFM of ventilation per 100 BTU is recommended.

 

The first part of this statement is not very helpful. The second part, however, provides some sort of guideline. Find out the BTUs, divide by 100, and you have a starting point.

 

The range is electric and, like the vent hood, it came with the house. My first stop is the owner's manual. Unfortunately there is no list of specifications. Looking the model up on the manufacturer's Web site, I find no mention of BTUs. Instead the burners are rated in watts.

 

Can watts be converted to BTUs? Since they are both units of energy, yes (we'll skip over the explanation that energy output ought to be expressed as watt-hours or BTUs per hour, but never is). One kilowatt-hour is equal to 3,412 BTUs per hour. So the 2,500 watts of my nine-inch burner is equal to 8,500 BTUs; the 1,500-watt burners are 5,118 BTUs; and the 2,000-watt, eight-incher is 6,824. All told, it comes to 25,560 BTUs. If I want to plan for a worst case, I need 256 CFM. Or do I?

 

I rarely, if ever, have all the burners cranked all the way up at the same time. If I had the two larger burners running at full blast, the 160 CFM supplied by the present fan should be sufficient. But the fact is that I can fill the house with smoke using only one burner turned up maybe 75%. The output of the burner is not really the issue; the issue is smoke and odor.

 

Be careful what you wish for

 

Let's look at it another way. My kitchen is 11 feet wide and about 14 feet long, and the ceiling is nine feet, making the volume of my kitchen 1,386 cubic feet. At 160 CFM, the air in my kitchen should be completely replaced in a little over eight and one-half minutes -- actually somewhat less, since a lot of volume is consumed by cabinetry and appliances. So what gives?

 

I assume that the manufacturer's label isn't lying. But maybe the rating is for the fan alone, without regard for the filter between the fan and the smoke, and the resistance of several feet of ductwork between the fan and the outside. Maybe the answer is to crank up the CFMs. Lots of people do -- it goes along with the fad for commercial-style ranges. Given the popularity of commercial-style cooktops featuring six or more burners rated at 15,000 to 18,000 BTUs, you might assume that these ranges require heavy duty ventilation -- up to 1,200 CFM. Indeed people do install such systems. Downdraft fans for small island cooktops start at a minimum of 600 CFM (partly because they have to fight convection). If a measly 160 CFM won't do the job, multiplying it by five or six ought to and probably will.

 

Imagine what happens to a 2000 square-foot room when you turn on a 1200 CFM ventilation fan. With eight-foot ceilings, the room would have a volume of 16,000 cubic feet, and the fan will revitalize the room’s air in 13 minutes. Where is the clean air going to come from? Answer: through the holes -- gaps in the floor, walls and windows. If the doors and windows are open, air movement is easy. But if it's recently built or remodeled housing, it has openings that are well weather-stripped, and a heating/ventilating/air-conditioning (HVAC) system that gets its air directly from the outside. In this case, air comes in through places where it isn't supposed to.

Air comes in through holes where it ought to be going out such as the fireplace, the furnace flue, and the water heater vents. This is air laden with exactly the sort of things you don't want in your house: carbon monoxide, oxides of nitrogen, and smoke particles. You might even spot a wisp or two of dryer lint along with anything that might be stuck to the inside of your furnace filters. A few pieces of lint are fine, but the rest is potentially very dangerous. It's called backdraft, and people die from it.

 

The easy solution is simply to open a nearby window (or two -- a 1200 CFM fan needs an opening about 24 inches in diameter), but this defeats the whole point of making the house tighter. While that fresh air (called make-up air in HVAC circles) is coming in, thirty years of advancement in home design and energy efficiency is leaking out -- just so you can rid yourself of a few cubic feet of noxiousness. We have to rethink this.

 

With great power comes great racket

 

Home kitchens aren't subject to the same regulations as commercial kitchens, and there are good reasons for this. A commercial kitchen must vent everything, including aerosolized grease, or risk creating significant fire hazards (or a stampede of patrons). One of the first things commercial kitchen novices remark upon is how noisy the lines are, and it's no surprise, given the 1 CFM/1K BTU guideline. Twelve 20K BTU burners means 2,400 CFM ventilation (and the required make-up air). It's like working in a wind tunnel.

 

Although change appears to be coming, few residential rules are included in the government regulations, and most are vague guidelines. One of the few specific directives available is from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). The applicable document is Standard 62-1989: Ventilation for Acceptable Indoor Air Quality. It prescribes an absolute minimum of 100 CFM, or 40 CFM per linear foot of cooking area. On that basis, a 30-inch range needs the minimum. OK, it's specific. But in the end it's not helpful, since my 160 CFM unit, at 60% above the requirement, is not doing the job.

 

The problem is that neither Broan nor ASHRAE address the real problem: you've got a source of smoke sitting in a specific spot, and you simply want to direct the smoke out of the house. So it's not an issue of power, it's an issue of control. One way to exert control is to make sure that the vent hood covers the entire cooking area, and take advantage of convection. Smoke, along with the hot air, will rise naturally to the fan intake. Island hoods do this job very well, since they usually match or exceed the cooktop in size. This coverage means that they can sit higher than the standard under-cabinet vent hood, which is usually 27 to 30 inches above the cooking surface or 63 to 66 inches above the floor. If the perimeter of an under-cabinet hood matched the cooking surface, anyone of average or above size would be banging their head against it with painful and annoying frequency.

 

The fact that a typical under-cabinet fan does not cover the entire cooking surface may not be significant for most cooks. It works for my Mom. A colleague of mine was surprised that I used one at all -- hers seems to be most useful as a microwave platform. But if you're still reading this, you are not most cooks. You stir-fry at extreme temperatures. You blacken fish in cast-iron skillets -- on purpose. You sear the edge fat on 2-inch-thick New York strips. But because you sometimes play with vacuum cleaners and shoeboxes, you have also learned that to remove smoke, brute force alone will not avail. The only avenue left is finesse. You have to make the smoke want to go where you want it to go. And as with children, spouses and co-workers, sometimes gentle pressure is most effective.

 

Pushmi-Pullyu

 

We learned from our shoebox experiment that negative pressure pulls things in (in the case of our shoebox, it tried to pull the walls in). This is how an exhaust fan works -- it creates an area of continuously regenerated negative pressure by removing the air in the vicinity of the fan. We can also infer the corollary: positive pressure pushes things away (imagine reversing the motor on your vacuum cleaner while it's still attached to the shoebox). So if we could create an area of positive pressure between the housing of the fan and the outer edge of the cooking surface, we could nudge the rising smoke into the negative pressure area, and it would go up the chimney. Luckily, we have a way to create a high-pressure area: we have a fan right there in our vent hood. With a little duct-work engineering, we can push air out on one side and suck it in at the other. As it turns out, Broan actually makes such a contraption -- the Allure.

 

And so we come to my original plan for this article. I am no Norm Abrams. I am not Handy Andy or Ty Pennington. I'm not even Tim Allen. My first attempt at appliance upgrade left us without a working toilet for three and a half days. That was twenty years ago, and I haven't improved much, except to recognize -- sometimes -- when it would be advisable to call for professional assistance. However, in fulfillment of my manly duties (and so I could go one up on the Magic Board), I set out to install a new vent hood. I expected the installation to be a disaster, but anything that involves power tools, hot air, and a legitimate chance to use duct tape for its intended purpose is too grand to pass up. At the least I would have a great farce for the Daily Gullet. But much to my surprise (and probably that of the rest of the household, though I am too proud to inquire), it works, and I accomplished the feat in less than a day.

 

I admit that I wasn't confident enough in my own grasp of physics to resist springing for the top-end, 400 CFM boost unit. But we don't use it. Score one for science.

 

 

Dave Scantland (aka Dave the Cook) is an Atlanta-based writer, graphic designer and cooking teacher. He is also director of operations for the eGullet Society for Culinary Arts & Letters.

 

[Jinmyo]

Dave, that's a great article! Very nice graphics as well.

[g.johnson]

Good article.

Want me to tell you the (trivial) physics errors now or later?

[Dave the Cook]

Good article.

Thanks.

Want me to tell you the (trivial) physics errors now or later?

Now, please.

[guajolote]

I was going to say that there is no such thing as negative pressure, but after googling I see that it is a commonly used term, especially in medicine (figures).

Edit: Very good article.

Edited February 12, 2003 by guajolote (log)

[vengroff]

Good article.

Thanks.

Want me to tell you the (trivial) physics errors now or later?

Now, please.

Here's a meteorological one: In a tornado, the low pressure is outside your house, so it pops like a balloon. It's just the opposite of what happens to the box when you vacuum out the air.

Otherwise a great article. I've been looking at ventilation (among other things, as I'm redoing an entire kitchen) and almost nobody I've talked to has any clue about the need for make-up airflow. They just point at the big high-CFM blowers and say they are better.

Also, regarding the noise issue, some manufactures offer remote blowers that sit outside the house at the end of the ductwork and suck the air out from there. Did your research turn up anything on these, or on how much is lost in the ductwork, based on cross section and length?

Edited February 12, 2003 by vengroff (log)

[g.johnson]

Very minor. Watts are a measure of power, i.e., the rate at which energy is generated with units of energy per unit time. BTU are a measure of energy. Therefore Watt-hours are a measure of energy and are equivalent to BTU. BTU per hour are a measure of power and are equivalent to Watts. The useful measurement in this case is power, Watts or BTU per hour.

[Dave the Cook]

Here's a meteorological one:  In a tornado, the low pressure is outside your house, so it pops like a balloon.  It's just the opposite of what happens to the box when you vacuum out the air.

I'm not sure where I've got it wrong. It's the extreme low pressure of the tornado that creates the suction. This is analogous to the vacuum cleaner on the outside of the box.

When you say "it pops like a balloon," you have it exactly right. A balloon doesn't explode, it implodes. The balloon skin collapses in on itself. The pop that we usually associate with an explosion is due to the violent outrush of air. Air in a balloon is slightly pressurized, just like a house. If you suddenly depressurize a house, it will collapse, not explode -- assuming associated high winds don't simply blow the house off its foundation.

If this isn't correct, please tell me where it goes off track.

Otherwise a great article. 

Thank you.

I've been looking at ventilation (among other things, as I'm redoing an entire kitchen) and almost nobody I've talked to has any clue about the need for make-up airflow.  They just point at the big high-CFM blowers and say they are better.

I hope I made the point that not only do you not necessarily need a lot of CFM, too much can cause a lot of trouble. I consulted friend of mine, who has been in HVAC for thirty years, and who I hoped would be a valuable resouce for the article. He turned out to be almost useless. Partly this was because he mainly does furnaces and AC, but also it was because no one had ever asked him. Once I started asking poited questions, he caught pretty quickly, but in the end, I think I taught him more than he taught me. There are tests you can do to check for depressurization and backdraft, but they're all post-installation. To figure it out ahead of time, you need to consult an HVAC person, not a kitchen person. They might not get it at first, but they will. They'll cough up lots of helpful charts and calculators, once you explain what you're after.

I didn't talk about dedicated make-up air (this is how many commercial kitchens handle the problem), but it's a viable option if you're doing extensive remodeling. In its simplest form, it's an opening to the outside that allows air in as necessary -- a hole in the wall. You can dress them up and add heaters and so forth. Apparently this is quite common in Canada.

Also, regarding the noise issue, some manufactures offer remote blowers that sit outside the house at the end of the ductwork and suck the air out from there.  Did your research turn up anything on these, or on how much is lost in the ductwork, based on cross section and length?

Here's what I know, or speculate (it's kind of spotty, because I didn't pursue this application):

1. You can't mess around with lots of turns and adapters that change the cross-section of the duct. These cause pressure changes and turbulence that can significantly affect fan performance.

2. I suspect (but don't know for sure) that lots of high-power fans get sold on the premise that you need more power due to the remote mounting. I think that this is misleading. If your ducts are well sealed, the only things that can cause suck reduction are turbulence caused by joints and turns, pressure drops due to poor duct design, and friction. You can minimize the first two; there's not much you can do about the third. But the main reason to have a honkin' big fan is to overcome the inertia (is this the right term?) of that long column of static air in the duct when the fan is not operating. Once this air is moving, a slightly bigger fan makes sense, but not a hugely bigger one. The important thing is to capture the air that you want to remove -- hood design is where it's at.

3. If you generate a lot of airborne grease, make sure you have a good filter. You can get into a vicious cycle here, as filters create resistance (something I didn't get into in the article). In general, better filters create more resistance, which creates the need for increased fan capacity. But there's a balance somewhere. I have also seen fan designs (one is here) that claim not to require filters, but none for remote installation.

The useful measurement in this case is power, Watts or BTU per hour.

Thanks. For some reason, I just find these terms too slippery to hold on to. Based on what you've written, I'm pretty sure that most of the EEs I work with are using it wrong, too. You couldn't by any chance explain reactive power (kVAR), could you?

[=Mark]

Great article, but being a lifelong weather nut I also have to chime in...

The folks involved in the weather service no longer advise to open a window to avoid damage from a tornado. 95% of the destructive force is from the windspeed, and the damage that can be attributed to the pressure difference happens much too quickly to be mitigated by a few open windows.

Another practice no longer advised when avoiding injury is that of taking refuge under overpasses when a tornato is approaching. Tests and actual incidents have shown that wind pressure can actually be increased when funneled under a highway overpass.

OK, back to food...

[g.johnson]

I had to look up reactive power since it’s an electrical engineering term, but it’s not difficult.

In electrical circuits you calculate the ‘apparent power’ by multiplying the current by the voltage. That would accurately represent the power you can get from an oven, for example. But in electrical circuits that contain capacitors and/or inductors some of the apparent power is stored in the circuit and is not available to do any work. That’s the reactive power. The power available for work, the ‘true power’, is equal the apparent power minus the reactive power. I guess it’s relevant for fans because they’re big inductors, so it’s important to consider true power.

[Dave the Cook]

I had to look up reactive power since it’s an electrical engineering term, but it’s not difficult.

In electrical circuits you calculate the ‘apparent power’ by multiplying the current by the voltage. That would accurately represent the power you can get from an oven, for example. But in electrical circuits that contain capacitors and/or inductors some of the apparent power is stored in the circuit and is not available to do any work. That’s the reactive power. The power available for work, the ‘true power’, is equal the apparent power minus the reactive power. I guess it’s relevant for fans because they’re big inductors, so it’s important to consider true power.

Actually, I didn't run across it my research.

I've been at this place (a major vendor of electric utility control software and hardware) for four years and I haven't been able to get any of the big brains around here to give me a decent explanation. Most of them just shrug.

Thanks. Your explanation was perfect. I may steal it. How do you suppose it came to be called "reactive"? Never mind -- has to do with reactance, doesn't it?

[g.johnson]

You've got it.

[Fat Guy]

In restaurants, one of the big issues is getting the swinging kitchen door to stay closed. If you don't get the ventilation right, it will always either be pulled inward or pushed outward. In the latter case kitchen smells will get into the restaurant. Not good unless you're trying to achieve a certain effect.

Those of us in apartment buildings have some unique ventilation issues. My roof vent, for example, is approximately 50 feet of duct away from my hood and who knows where the vaporized grease is re-collecting (fire safety in hood design is a very interesting issue I studied a bit when I did my installation). Then again, a long rise like that creates a natural suction effect that is quite powerful -- so much so that very often in an apartment situation the ductwork is a far more significant issue than the blower.

[stellabella]

no one said anything about the STEAKS. thanks for the inspiration, big boy.

another great piece from another great atlantan.

[=Mark]

In restaurants, one of the big issues is getting the swinging kitchen door to stay closed. If you don't get the ventilation right, it will always either be pulled inward or pushed outward. In the latter case kitchen smells will get into the restaurant. Not good unless you're trying to achieve a certain effect.

I've known establishments where the opposite was a problem, excessive venting was pulling heated/air conditioned air out of the dining room.

Those of us in apartment buildings have some unique ventilation issues. My roof vent, for example, is approximately 50 feet of duct away from my hood and who knows where the vaporized grease is re-collecting (fire safety in hood design is a very interesting issue I studied a bit when I did my installation). Then again, a long rise like that creates a natural suction effect that is quite powerful -- so much so that very often in an apartment situation the ductwork is a far more significant issue than the blower.

This was touched on in one of the "Blue Smoke" threads. After they had installed their smoker, the draft from the 15 story high chimmney resulted in a situation in the device more akin to a blast furnace than a food smoker. Several dampers had to be installed and tuned to achieve the correct airflow.

[Dave the Cook]

no one said anything about the STEAKS.  thanks for the inspiration, big boy.

another great piece from another great atlantan.

Thanks, Stella.

The steaks were a reward and a test. Prior to the new hood, this sort of prep filled the house with smoke; Mrs. Dave, the girl and Thing 2 would walk around with those Home Depot-style dust masks, giving me the evil eye. After a couple of evenings of feeling like I lived in Northern Iraq, I just gave up trying to cook steak unless I could grill it outdoors.

But I think the photo shows that the fan works pretty well. In the interest of full disclosure, I should admit that when I do that edge-fat thing (which I hadn't tried at the time I took the picture), I do have to use the boost mode.

[col klink]

I have a friend who just built a new house in Canada and they installed the vents with the fans at the exterior. They were extremely quiet and totally cool. They were operated by wall switches that reacted to close movements and kept the fan on for 7 minute increments up to 28. I was extremely jealous. They operated as well as standard air fans.

[vengroff]

The folks involved in the weather service no longer advise to open a window to avoid damage from a tornado.  95% of the destructive force is from the windspeed, and the damage that can be attributed to the pressure difference happens much too quickly to be mitigated by a few open windows. 

I saw the same thing when I looked on the web. Guess it's been too long since I lived in the tornado belt. Re: the wind, are structures generally pushed over by it, or does it peel the roof off first? If the latter, isn't this just a Bernoulli effect, which is really just low pressure caused by high wind speed?

The point I was trying to make about the tornado and house case vs. the vacuum and box case is that in the tornado case, the high pressure is inside the house and the low pressure is outside, whereas in the vacuum case the low pressure is inside the box and the high pressure is outside.

[vengroff]

I have a friend who just built a new house in Canada and they installed the vents with the fans at the exterior. They were extremely quiet and totally cool. They were operated by wall switches that reacted to close movements and kept the fan on for 7 minute increments up to 28. I was extremely jealous. They operated as well as standard air fans.

That sounds great! Do you know who the manufacturer is?

[maggiethecat]

Archie: Thanks for this piece. Extremely timely, because our current ventilation has decided to give up and die. I printed it out for further perusal and everything.

And we have matching pans.

[Dave the Cook]

In restaurants, one of the big issues is getting the swinging kitchen door to stay closed. If you don't get the ventilation right, it will always either be pulled inward or pushed outward. In the latter case kitchen smells will get into the restaurant. Not good unless you're trying to achieve a certain effect.

I've known establishments where the opposite was a problem, excessive venting was pulling heated/air conditioned air out of the dining room.

This happened in the first restaurant I worked in. The solution was to prop open the back door, which was just down the hall from the loading dock. The hall was used to stage food for banquets, which were served in adjacent ballrooms. At times, we'd get a 10 - 15 mph wind through the hall; if we closed the dock door, air got pulled from the banquet rooms. Doesn't sound like much, but when it's indoors, a breeze that stiff can be disconcerting. It made the hall useless for staging in the winter, because the food would go cold.

[tsquare]

Pray tell, what fan did you install? and what do you mean by "we don't use it"? Did you install 400 cfm and only turn it on low?

In the State of Washington, we are instructed to "build it tight, ventilate it right". Indoor Air Quality code dictates a minimum of 100 cfm for range hoods, 50 cfm minimum for bathrooms, laundries and other sources of water vapor, and whole house fans to match the amount of square feet and number of bedrooms (all those annoying sleepers breathing out moisture all night long.) In addition, there is supposed to be a source of fresh air - ports in window frames or through wall in each habitable room. Alternately, a whole house filtered ventilation system can be substituted.

[col klink]

That sounds great!  Do you know who the manufacturer is?

Not off the top of my head, but I can find out for you.

[MsRamsey]

In the State of Washington, we are instructed to "build it tight, ventilate it right".

But it doesn't always happen. My smoke alarm goes off WHEN I BOIL WATER. And my building isn't old.

[Dave the Cook]

Pray tell, what fan did you install? and what do you mean by "we don't use it"? Did you install 400 cfm and only turn it on low?

In the State of Washington, we are instructed to "build it tight, ventilate it right". Indoor Air Quality code dictates a minimum of 100 cfm for range hoods, 50 cfm minimum for bathrooms, laundries and other sources of water vapor, and whole house fans to match the amount of square feet and number of bedrooms (all those annoying sleepers breathing out moisture all night long.) In addition, there is supposed to be a source of fresh air - ports in window frames or through wall in each habitable room. Alternately, a whole house filtered ventilation system can be substituted.

Sorry if I wasn't clear. Here's what we installed:

The Broan Allure III.

It has four fan speeds. The highest speed, called "Boost" moves 400 CFM. At the time I wrote the article, I had not used it. Since then I have, once for searing the fat on steaks and once (again for searing edge fat) on lamb loin chops. Otherwise, it rarely goes above the second setting. It claims to have an automatic feature that sets the fan speed if the heat get too high, but this has never kicked in. I recommend it, with the warning that in Boost mode, it's quite noisy.

But I should also say that I think a lot of the noise is due to the duct work that had been installed when the house was built. I originally wanted to do a remote installation like Vengroff is contemplating, but the way the ducts had been installed, I would have had to do extensive work on a load-bearing wall. Neither my budget nor my skills would have stood for that, though I thought about holding out for a medical "prescription" that would have let us deduct part of the cost, due to the respiratory difficulties I mentioned.

The other option (sort of) available was to install a hood that mirrored the footprint of the stovetop. Aesthetically, this was very appealing. But again, whoever did the original installation vexed me. I'll have to wait for a full remodeling. Look for a report when Thing 2 graduates from college. This should be on or about 2013.

Washington is one of the few states that has any regulations whatsoever, so you should feel at least a little lucky. Their guidelines seem to be base on Cnadiam standards, which have some thinking behind them. Not enough, IMHO, but at least it's a point on the checklist.

Most states don't check for it at all. They check only HVAC, and that, in my experience of buying five houses (all of them new construction) in twelve years, is cursory at best. This is a business that is very much a "good 'ol boys" club. As Ms. Ramsey alludes, sometimes you win, sometimes you lose, sometimes it rains.*

tsquare, if you need further information, PM me and I will forward what I have to you.

*Thanks to Ron Shelton, "Bull Durham"